Flow meters for indicating the rate of liquid flow through a conduit are known in various forms. In most flow measurement applications, a flow meter must be configured so that it can distinguish among various flow rates along a continuous flow rate spectrum (e.g. between 1 and 10 gallons per minute (gpm)).
Two flow meters that are capable of indicating flow rates along a spectrum are described in U.S. Pat. Nos. 4,523,464 and 3,001,397. Each of these two meters relies on a liquid level within a measurement chamber having a restricted outlet at its lower end. The liquid level within the chamber is associated with a specific outlet flow rate.
In other applications, it is advantageous if only a small number of flow rates, as opposed to a continuous spectrum of rates, is indicated. For example, in oil reclamation applications in which a portion of total oil flow in an engine system is routed for liquid and solid decontamination, there may only be a small ideal range of flow rates (e.g. between three and four gpm).
In these applications, a preferred meter should operate in a distinct and easily identifiable manner when the flow rate is within the ideal range so that an observer can easily identify if the flow rate is within the ideal range. The flow indication should be rugged in operation and not readily susceptible to extreme fluctuations that may be induced by viscosity changes, system vibrations and other factors. To this end, a large change in indicator status when the flow rate transitions into or out of an acceptable range, rather than minute, incremental changes to slight variations in flow rate, is particularly advantageous.
Unfortunately, the meters described in the patents referenced above operate in the same manner regardless of flow rate. As flow rate increases, liquid level increases. In some embodiments, as flow rate increases, the liquid level rate of increase decreases. Thus, these meters are incapable of providing a large, quantum change in indicator status when the flow rate transitions into or out of an acceptable range.
In these meters differences in liquid viscosity (viscosity results in shearing stress caused by flow velocity) dramatically affect flow rate. For this reason these meters must be calibrated to account for the specific viscosity of the liquid passing therethrough.
Moreover, liquid viscosity can change as a function of ambient conditions, such as temperature. For example, the shear stresses associated with oil at a low temperature are greater than the stresses at a high temperature. Because the meters above must be calibrated as a function of liquid viscosity, where liquid viscosity changes, the meters would be inaccurate unless recalibrated.
Therefore, it would be advantageous to have an oil flow rate meter that could provide a large change in indicator status when the flow rate transitions into or out of an acceptable range and that can operate relatively accurately despite different oil viscosities, temperature variations and other environmental fluctuations.